To produce a ruthenium thin film or a ruthenium compound thin film by a chemical deposition method such as a chemical vapor deposition method (CVD method) or an atomic layer deposition method (ALD method), various organoruthenium compounds have been hitherto known as a raw material for a thin film. One of the organoruthenium compounds for which practical application is recently investigated is dodecacarbonyl triruthenium having a following formula (hereinbelow, referred to as DCR).

DCR is a substance, which has a melting point of 154 to 155° C. and present as a solid (orange crystal) at normal temperature. DCR has a simple molecular structure, which contains Ru and CO and can be formed into a film only by thermal decomposition without any use of reaction gas. As DCR scarcely leaves an impurity such as a hydrocarbon in a thin film, and although it is a solid raw material, regulation of the specification of the raw material vessel or an appropriate process control does not adversely affect the production efficiency of a thin film, a further application of DCR is expected.
Examples of a method for producing DCR include a method in which a ruthenium compound is carbonylated to obtain crude DCR and the crude DCR is purified to DCR by sublimation, recrystallization, column chromatography, or the like (Patent Document 1). The crude DCR obtained by synthesis of a ruthenium compound contains a trace amount of impurity elements such as iron (Fe), aluminum (Al), and chrome (Cr), and thus purification is necessary after the synthesis, because the impurity elements may cause, at the time of formation of a ruthenium thin film, an ignition phenomenon even when it is contained in a trace amount.
As a purification means for lowering the impurity elements contained in DCR, a sublimation method is effective among the methods described above. That is because, since DCR easily sublimes at reduced pressure, DCR with high purity can be produced by use of a difference in sublimation rate compared to the impurity elements.